1. Field of the Invention
This invention relates to a process for preparing a poly(paraphenylene terephthalamide) fibrous gel composition comprising an amide solvent, an alkaline earth metal salt and N-methylpyrrolidine or its hydrochloride and a process to prepare wholly poly(paraphenylene terephthalamide) papers using the composition as a binder.
2. Description of the Prior Art
The preparation of poly(paraphenylene terephthalamide) such as taught by U.S. Pat. No. 3,869,429 issued to Blades is generally described by reacting terephthaloyl chloride with para-phenylenediamine in a stirred solution of an alkaline earth metal salt and an amide solvent such as N-methylpyrrolidone. The result is a dry, crumb-like product devoid of fiber structure and too coarse for fiber or paper uses. To make fibers, the polymer component must be isolated from the reaction product by, for example, washing and drying, then dissolving the polymer in an appropriate solvent such as sulfuric acid and spinning the solution through an air gap into a coagulation bath.
Poly(paraphenylene terephthalamide) pulp is generally prepared from such spun filaments which are washed and dried before mechanical abrasion into pulp. It is also generally necessary to use specialized fiber cutting equipment to cut the spun continuous filaments into uniform short lengths before abrasion into pulp.
Obtaining poly(paraphenylene terephthalamide) polymers useful as a pulp directly from the polymerization system without first spinning a fiber is disclosed in U.S. application Ser. No. 07/213,741 filed June 30, 1988. Briefly, that process for producing para-aramid pulp includes forming an actively polymerizing solution containing para-aramid polymer chains by contacting an aromatic diacid halide and an aromatic diamine in a solvent and subjecting the solution to orienting flow. When the solution has a viscosity sufficient to maintain the orientation of the polymer chains, the solution is incubated until it gels. The gel is cut and the pulp is isolated from the gel.
The use of an acid acceptor in a polymerization system is known. As examples, U.S. Pat. No. 4,011,203 issued Mar. 8, 1977 and U.S. Pat. No. 4,072,664 issued on Feb. 7, 1978 disclose processes to prepare copolymers of two aromatic polyamides optionally using an acid acceptor as a polymerizing additive. Suitable acid acceptors for polymerizing the aromatic polyamides produced from one of piperazine, p-phenylene diamine, terephthaloyl halide or N,N'-bis(p-aminobenzoyl) ethylene diamine may include N-methylpyrrolidine and N-methylmorpholine present in an amount of not more than 10% by volume based on the volume of the solvent in the polymerization system.
Aromatic tertiary amines, such as pyridine are disclosed in references teaching the preparation of aromatic polyamides. For example, Japanese Pat. Application No. 52-124099 published Oct. 18, 1977 discloses a method of preparing aromatic polyamides using as polymerizing additives only aromatic tertiary amines. U.S. Pat. No. 4,511,623 issued Apr.16, 1985 discloses poly(paraphenylene terephthalamide) short fibers directly prepared during polymerization of the components of the polymer. Only heterocyclic aromatic tertiary amines such as pyridine, are taught as suitable additives to achieve the desired chain growth. Similarly, U.S. Pat. No. 4,579,895 issued Apr.1, 1986 to Cuidard, et al. discloses a process to prepare poly(paraphenylene terephthalamide) using tertiary amines with a pKa equal to, at most, 6.60 such as pyridine. Cuidard et al. discloses that the use of an amine with a higher pKa forms a sparingly soluble complex between the tertiary amine and the terephthaloyl chloride, totally or partially preventing the terephthaloyl chloride from reacting with the para-phenylenediamine.